3499 research outputs found
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(A cura di) The power state is back? The evolution of russian political thought after 1991
No full textHow to estimate epidemic risk from incomplete contact diaries data?
No full textSocial interactions shape the patterns of spreading processes in a population. Techniques such as diaries or proximity sensors allow to collect data about encounters and to build networks of contacts
between individuals. The contact networks obtained from these different techniques are however quantitatively different. Here, we first show how these discrepancies affect the prediction of the
epidemic risk when these data are fed to numerical models of epidemic spread: low participation rate, under-reporting of contacts and overestimation of contact durations in contact diaries with
respect to sensor data determine indeed important differences in the outcomes of the corresponding simulations with for instance an enhanced sensitivity to initial conditions. Most importantly, we
investigate if and how information gathered from contact diaries can be used in such simulations in order to yield an accurate description of the epidemic risk, assuming that data from sensors represent the ground truth. The contact networks built from contact sensors and diaries present indeed several structural similarities: this suggests the possibility to construct, using only the contact diary network information, a surrogate contact network such that simulations using this surrogate network give the same estimation of the epidemic risk as simulations using the contact sensor network. We present and compare several methods to build such surrogate data, and show
that it is indeed possible to obtain a good agreement between the outcomes of simulations using surrogate and sensor data, as long as the contact diary information is complemented by publicly
available data describing the heterogeneity of the durations of human contacts
A continuous-time stochastic model for the mortality surface of multiple populations
No full textWe formulate, study and calibrate a continuous-time model for
the joint evolution of the mortality surface of multiple populations. We model
the mortality intensity by age and population as a mixture of stochastic latent
factors, that can be either population-specific or common to all populations.
These factors are described by affine time-(in)homogenous stochastic processes.
Traditional, deterministic mortality laws can be extended to multi-population
stochastic counterparts within our framework. We detail the calibration pro-
cedure when factors are Gaussian, using centralized data-fusion Kalman filter.
We provide an application based on the mortality of UK males and females.
Although parsimonious, the specification we calibrate provides a good fit of
the observed mortality surface (ages 0-99) of both sexes between 1960 and
2013
Design of acoustic metamaterials through nonlinear programming
No full textThe dispersive wave propagation in a periodic metamaterial with tetrachiral topology and inertial local resonators is investigated. The Floquet-Bloch spectrum of the metamaterial is compared with that of the tetrachiral beam lattice material without resonators. The resonators can be designed to open and shift frequency band gaps, that is, spectrum intervals in which harmonic waves do not propagate. Therefore, an optimal passive control of the frequency band structure can be pursued in the metamaterial. To this aim, a suitable constrained nonlinear optimization problem on a compact set of admissible geometrical and mechanical parameters is stated. According to functional requirements, the particular set of parameters which determines the largest low-frequency band gap between a pair of consecutive branches of the Floquet-Bloch spectrum is obtained. The optimization problem is successfully solved by means of a version of the method of moving asymptotes, combined with a quasi-Monte Carlo multi-start technique.
Subjects: Materials Science (cond-mat.mtrl-sci)
Cite as: arXiv:1603.07717 [cond-mat.mtrl-sci]
(or arXiv:1603.07717v2 [cond-mat.mtrl-sci] for this version
Dynamic Adverse Selection and the Supply Size
No full textIn this paper we examine the problem of dynamic adverse selection in a stylized market where the quality of goods is a seller's private information while the realized distribution of qualities is public information. We obtain that full trade occurs in every dynamic competitive equilibrium. Moreover, we show that if prices can be conditioned on the supply size then a dynamic competitive equilibrium always exists, while it fails to exist if prices cannot be conditioned on the supply size and the frequency of exchanges is high enough. We conclude that the possibility to condition prices on the supply size allows to reach efficiency in the limit for exchanges becoming more and more frequent, while otherwise the welfare loss due to delays of exchanges remains bounded away from zero
La rilevanza e i caratteri degli aspetti psicologici nella conduzione dell'azienda familiare
No full textNelle conduzione delle aziende familiari si intrecciano elementi tipici della psicologia del lavoro e delle organizzazioni con altri di natura familiare, sistemiche di relazione interpersonale normalmente non presenti o comunque poco rilevanti nelle altri situazioni aziendali. II capitolo fornisce alcune chiavi interpretative mediante la lettura delle proposte formulate dalle scuole di pensiero psicologico più significative combinate con la prospettiva di analisi economico aziendale
Model Predictive Control of Nonholonomic Mobile Robots Without Stabilizing Constraints and Costs
No full textThe problem of steering a nonholonomic mobile robot to a desired position and orientation is considered. In this paper, a model predictive control (MPC) scheme based on tailored nonquadratic stage cost is proposed to fulfill this control task. We rigorously prove asymptotic stability while neither stabilizing constraints nor costs are used. To this end, we first design suitable maneuvers to construct bounds on the value function. Second, these bounds are exploited to determine a prediction horizon length such that the asymptotic stability of the MPC closed loop is guaranteed. Finally, numerical simulations are conducted to explain the necessity of having nonquadratic running costs
Real Options and Incremental Search in Pharmaceutical R&D Project Portfolio Management
No full textThis paper investigates the role of real options reasoning in R&D project portfolio management and investment decisions of pharmaceutical firms. We analyse a unique dataset that integrates information on initiation and termination of clinical trials at the level of specific medical indications. Consistent with existing literature, we find a positive relationship between market size and firm entry in clinical trials. We also show that the option value of R&D investments, as proxied by the scope of R&D projects, affects the selection of target markets. Moreover, high-risk research areas attract more entry, in line with the predictions of real options theory. However, we also find that more flexibility in project duration and delayed project discontinuation attract higher rates of entry. Departures from pure real options reasoning are motivated by the presence of incremental learning in pharmaceutical R&D
A two-scale constitutive parameters identification procedure for elasto-plastic fracture
No full textConstitutive parameters identification for elasto-plastic fracture is a complex problem due to the interplay between two forms of material nonlinearity, viz. plasticity and cohesive fracture. In the present study we examine this problem in relation to Copper specimens covered by Silver used in photovoltaic modules as electrical conductors. Uniaxial tensile tests on un-notched and notched specimens are performed with a tensile stage inside a scanning electron microscope, monitoring crack growth for each imposed far-field displacement. Parameters identification is then performed by considering an elasto-plastic constitutive relation with isotropic hardening for the continuum and a polynomial cohesive zone model (CZM) with two free parameters. For a better numerical-experimental fitting, a four-parameter CZM should be used to independently control the CZM stiffness and the fracture energy. To do so effectively, a constrained optimization procedure with a two-scale objective function is outlined